The major aim of this proposal is to examine the role of vasopressin secreting neurons in the supra-optic nucleus on the maintenance and development of hypertension. Secondary aims are the establishment of the validity of the physiological criteria for identifying vasopressin neurons and the identification of afferent nuclei and pathways to the supra-optic nucleus. The methodologies to be used will be single unit electrophysiological techniques, histological analysis and modulations of organs and fluid content of the cardiovascular system. These experiments will be carried out on normotensive and hypertensive preparations.